In various fields such as the electric/electronic component field, a tendency toward lower halogenation as an effort to the environment has recently been increased.
Polyarylene sulfide resins (may be abbreviated as “PAS” hereinafter) represented by polyphenylene sulfide resins (may be abbreviated as “PPS” hereinafter) attract attention as halogen-free materials because flame retardancy can be satisfactorily achieved without using a halogen-based flame retardant.
The polyarylene sulfide resins can be generally produced by polymerization reaction in an organic polar solvent using p-dichlorobenzene, sodium sulfide or sodium hydrosulfide and sodium hydroxide as raw materials (refer to Patent Literatures 1 and 2). Currently commercially available polyarylene sulfide resins are produced by this method, but the method not only requires a purification process for removing the organic polar solvent used in a production process and by-products such as sodium chloride but also leaves chlorine atoms remaining in the resins even after purification treatment.
Therefore, there is known a method for producing a polyarylene sulfide resin by melt polymerization using a diiodo aromatic compound and elemental sulfur without using chlorine atoms and a polar solvent (refer to Patent Literatures 3 and 4). This method can produce a polyarylene sulfide resin containing iodine atoms but can remove iodine atoms by sublimation by heating a polymerization reaction product or a reaction mass after polymerization reaction under a reduced pressure, thereby suppressing an iodine concentration in the resin. However, the method uses elemental sulfur (S8) as a polymerization raw material, and thus a disulfide bond (—S—S—) remains in a skeleton of the finally resultant polyarylene sulfide resin, thereby causing deterioration in thermal characteristics and mechanical characteristics.
Therefore, a method for producing a polyarylene sulfide resin by melt polymerization of a mixture containing a diiodo compound, solid sulfur, and a sulfur-containing polymerization inhibitor has been developed (refer to Patent Literature 5). However, this method has the problem that the polyarylene sulfide resin produced by the method has low reactivity to other compounds and resins. Therefore, when an impact resistance improver such as an epoxysilane coupling agent, a functional group-containing thermoplastic elastomer, or the like is added to the polyarylene sulfide resin, the effect of improving impact resistance cannot be satisfactorily obtained, and thus application and using methods are limited.